The present disclosure relates to the subject matter contained in Japanese Patent Application No.2001-214602 filed on Jul. 16, 2001, which is incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates to an ink jet printer and a printing method and particularly to an ink jet printer and a printing method which perform bidirectional printing on a sheet using a head for ejecting inks of a plurality of colors.
2. Description of the Related Art
As an apparatus for outputting a digital color image, a color inkjet printer having inks of a plurality of colors has been proposed. Such an apparatus is widely used for printing an image. In an inkjet printer, while a head in which a plurality of nozzles are integrally arranged is moved in a direction (main scanning direction) perpendicular to a direction (sub-scanning direction) along which a printing medium such as a paper sheet is fed, ink particles ejected from the nozzles of the head are impacted on the printing medium, thereby forming ink dots on the medium to record an image. Inks of black (K), cyan (C), magenta (M), and yellow (Y) are used as those of basic colors.
In such an inkjet printer, in order to improve the printing speed, bidirectional printing is performed, i.e., ink ejection while moving the head in the main scanning direction is conducted in both the forward and reverse directions of the head. In the case of the bidirectional printing, when inks are impacted on the printing medium in the forward direction in the color sequence of KCMY, inks are impacted on the printing medium in the reverse direction in the opposite color sequence of YMCK.
This difference in color sequence of impacting inks causes a problem in that the hue is delicately varied because of the reason that will be described below. In the case where blue (B) is formed by inks of C and M, for example, the color tone of B which is formed in the forward direction in the color sequence of C and M is delicately different from that of B which is formed in the reverse direction in the color sequence of M and C. This causes the problem in that, although B of a uniform hue is originally to be printed, B is printed in color tones which are different from each other in a stripe-like manner along the main scanning direction.
In order to solve the problem, in JP-B-3-77066 and JP-A-8-295034, a printing method has been proposed in which heads or nozzles are disposed independently for the forward direction (for example, the sequence of KCMY) and the reverse direction (for example, the sequence of YMCK), thereby equalizing the color sequences of impacting inks with each other.
By contrast, JP-A-11-207999 discloses a printing method to be employed in an inkjet recording method in which inks are ejected in both the forward and reverse paths in the main scanning direction by using an inkjet head wherein nozzle groups each for different colors are arranged in the print operation direction (main scanning direction), and sub scanning is performed between the forward path and the reverse path, or between the reverse path and the forward path, thereby forming an image on a printing medium. In the printing method, when an image is to be formed on a printing medium by using a mixed color based on inks of different colors, an ink which is applied lately in the forward direction of the main scanning is ejected in an ejection amount smaller than an ink which is applied early, in both the forward and reverse paths. According to the printing method disclosed in the related art, a difference between displayed colors in the forward and reverse paths is eliminated to enable bidirectional printing in an inkjet printer.
In the printing method according to the related art disclosed in JP-B-3-77066 and JP-A-8-295034, the nozzle head for the reverse direction is not used in the forward direction, and that for the forward direction is not used in the reverse direction, thereby causing a problem in that, in order to realize the same printing speed as that in a conventional method, nozzles and heads which are twice in number are required.
By contrast, the printing method according to the related art disclosed in JP-A-11-207999 has a problem in that an adverse effect is produced depending on a printing medium to enhance the variation in hue. This is caused by the phenomenon that the manner of hue variation in bidirectional printing depends on a printing medium. Namely, the direction of hue variation in a printing medium into which an ink easily penetrates, such as recycled paper, plain paper, or coated paper is different from that in a printing medium into which an ink hardly penetrates, such as glossy paper, or an OHP sheet. This will be described by way of an example in which B is formed by C and M.
In a printing medium into which an ink easily penetrates, an ink of C which is early impacted stays in the surface and the inside of the medium, and an ink of M which is lately impacted penetrates so as to move round below the ink of C, so that a hue in which C that is early impacted is stronger is obtained. In a printing medium into which an ink easily penetrates, namely, the color of an ink that is early impacted is dominant. By contrast, in a printing medium into which an ink hardly penetrates, an ink of C that is early impacted stays in the surface of the medium, and an ink of M which is lately impacted flows onto the ink of C or a portion where the ink of C is not placed, so that a hue in which M that is lately impacted is stronger is obtained. In a printing medium into which an ink hardly penetrates, namely, the color of an ink that is lately impacted is dominant.
Therefore, the printing method which is disclosed in JP-A-11-207999 in which the ejection amount of an ink that is lately printed is made smaller is effective for a printing medium into which an ink hardly penetrates, and in which the color of an ink that is lately impacted is dominant. In the method, for a printing medium into which an ink easily penetrates, and in which the color of an ink that is early impacted is dominant, however, the color of the ink that is early impacted is stronger, or an adverse effect is produced.
Usually, glossy paper that is a printing medium into which an ink hardly penetrates is used in printing in which the image quality is more significant than the printing speed. In contrast, recycled paper, plain paper, or the like that is a printing medium into which an ink easily penetrates is used in printing in which the printing speed is more significant than the image quality. Bidirectional printing is performed in order to improve the printing speed. Therefore, the countermeasure against the above-mentioned problem of hue variation in bidirectional printing is more important in a printing medium into which an ink easily penetrates. As described above, however, the printing method according to the related art which is disclosed in JP-A-11-207999 has the problem in that the variation in hue is enhanced in recycled paper, plain paper, or the like which are subjected to bidirectional printing with a higher possibility.
The variation in hue appears in different manners depending on the mode of filling a printed region with dots. A head in which the density of nozzles (hereinafter, referred to as nozzle density) in the sub-scanning direction is equal to the dot recording density (dpi) on a printing medium will be considered. In the case where an image of a region of (the length of a nozzle row in the sub-scanning direction)xc3x97(the moving distance of the head in the main scanning direction) (hereinafter, such a region is referred to as raster) is formed by one movement of the head in the main scanning direction (hereinafter, such recording is referred to as one-pass raster recording), the hue variation in bidirectional printing appears alternately or for each raster, and hence is conspicuous.
In the case where an image for one raster is formed by plural reciprocal movements in the main scanning direction by using a similar head (hereinafter, such recording is referred to multi-pass recording), bidirectional printing allows dots of different hues to be printed in an alternate manner of a high frequency in the main scanning direction, and hence the variation in hue can be made inconspicuous. In such multi-pass recording, the number of scanning operations is larger than that in the one-pass recording, and hence there is a problem in that the printing speed is low.
In the case of a head in which the nozzle density is lower than the dot recording density (dpi) on a printing medium, dots for the recording density in the sub-scanning direction cannot be formed by one movement in the main scanning direction, and therefore the main scanning is performed several times (hereinafter, such recording is referred to as interlace recording). In this case, lines of different hues which are formed in the main scanning direction by bidirectional printing are formed in an alternate manner of a high frequency in the sub-scanning direction, and hence the variation in hue is hardly perceived.
In the multi-pass recording and the interlace recording, as compared with the one-pass raster recording, the speeds of dots which are impacted at one time on a printing medium are different. Therefore, inks penetrate in different manners, so that not only the easiness of perception of the variation in hue, but also the degree of the variation in hue are changed. Among printing media, or paper which is usually called recycled paper, factors such as the ratio of recycled pulp and the addition amount of a surface processing agent are different, and therefore inks penetrate in different manners. As described above, the hue variation due to bidirectional printing is different depending on the kind of a printing medium and the recording method, and therefore it is difficult to completely eliminate the hue variation.
The invention has been conducted in view of the above-discussed problems. It is an object of the invention to provide a printing apparatus and a printing method in which the hue variation in an image produced by bidirectional printing can be reduced irrespective the kind of a printing medium, a recording medium on which a program for the method is recorded, and a program.
In order to attain the object, according to a first aspect of the invention, there is provided an ink jet printer including a print head, a detection section, and a first control section. The print head has a nozzle array extending in a sub scanning direction. The nozzle array is arranged in a main scanning direction for each color. The print head reciprocally moves in the main scanning direction to print on a recording medium in both forward and reverse directions. The detection section detects a moving direction of the print head in the main scanning direction. The first control section increases an amount of an ink of a lately ejected color in comparison with an amount of an ink of a early ejected color irrespective of the moving direction of the print head detected by the detection section, when printing an image on the recording medium using a mixed color.
According to a second aspect of the invention, there is provided an ink jet printer including a print head, a hue changing degree storage section, a recording medium specifying section, a scanning pattern section, a hue changing degree determining section, and a data conversion section. The print head has a nozzle array extending in a sub scanning direction. The nozzle array is arranged in a main scanning direction for each color. The print head reciprocally moves in the main scanning direction to print on a recording medium in both forward and reverse directions. The hue changing degree storage section stores hue of each color in the forward and reverse directions at a time of printing an image on a recording medium with a mixed color. The recording medium specifying section determines a kind of the recording medium. The scanning pattern section determines a scanning pattern in the main scanning direction of the print head based on a recording mode inputted from external. The hue changing degree determining section refers the hue changing degree storage section to determine the hue changing degree of each color based on the determined kind of the recording medium and the determined scanning pattern. The data conversion section converts image data to be printed based on the determined hue changing degree.
According to a third aspect of the invention, there is provided a printing method using a print head. The print head has a nozzle array extending in a sub scanning direction. The nozzle array is arranged in a main scanning direction for each color. The print head reciprocally moves in the main scanning direction to print on a recording medium in both forward and reverse directions. The printing method includes the steps of detecting a moving direction of the print head in the main scanning direction and increasing an amount of an ink of a lately ejected color in comparison with an amount of an ink of a early ejected color irrespective of the detected moving direction of the print head, when printing an image on the recording medium using a mixed color.
According to a fourth aspect of the invention, there is provided a printing method using a print head. The print head has a nozzle array extending in a sub scanning direction. The nozzle array is arranged in a main scanning direction for each color. The print head reciprocally moves in the main scanning direction to print on a recording medium in both forward and reverse directions. The method includes the steps of determining a kind of the recording medium, determining a scanning pattern in the main scanning direction of the print head based on a recording mode inputted from external, referring hue changing degree storage means for storing hue of each color in the forward and reverse directions at a time of printing an image on a recording medium with a mixed color, to determine the hue changing degree of each color based on the determined kind of the recording medium and the determined scanning pattern, converting image data to be printed based on the determined hue changing degree.